diff --git a/Cargo.lock b/Cargo.lock
index 634480e5fb..61fd24ef7f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1771,7 +1771,6 @@ dependencies = [
 name = "xtask"
 version = "0.1.0"
 dependencies = [
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "pico-args 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/xtask/Cargo.toml b/xtask/Cargo.toml
index 4fc1c744bf..023f6a859f 100644
--- a/xtask/Cargo.toml
+++ b/xtask/Cargo.toml
@@ -7,7 +7,6 @@ publish = false
 
 [dependencies]
 walkdir = "2.1.3"
-itertools = "0.8.0"
 pico-args = "0.3.0"
 quote = "1.0.2"
 proc-macro2 = "1.0.1"
diff --git a/xtask/src/codegen/gen_parser_tests.rs b/xtask/src/codegen/gen_parser_tests.rs
index e09b6fcfec..0f550d9488 100644
--- a/xtask/src/codegen/gen_parser_tests.rs
+++ b/xtask/src/codegen/gen_parser_tests.rs
@@ -7,8 +7,6 @@ use std::{
     path::{Path, PathBuf},
 };
 
-use itertools::Itertools;
-
 use crate::{
     codegen::{self, update, Mode},
     project_root, Result,
@@ -61,38 +59,45 @@ struct Tests {
 fn collect_tests(s: &str) -> Vec<(usize, Test)> {
     let mut res = vec![];
     let prefix = "// ";
-    let comment_blocks = s
-        .lines()
-        .map(str::trim_start)
-        .enumerate()
-        .group_by(|(_idx, line)| line.starts_with(prefix));
+    let lines = s.lines().map(str::trim_start).enumerate();
 
-    'outer: for (is_comment, block) in comment_blocks.into_iter() {
-        if !is_comment {
-            continue;
+    let mut block = vec![];
+    for (line_idx, line) in lines {
+        let is_comment = line.starts_with(prefix);
+        if is_comment {
+            block.push((line_idx, &line[prefix.len()..]));
+        } else {
+            process_block(&mut res, &block);
+            block.clear();
         }
-        let mut block = block.map(|(idx, line)| (idx, &line[prefix.len()..]));
+    }
+    process_block(&mut res, &block);
+    return res;
 
+    fn process_block(acc: &mut Vec<(usize, Test)>, block: &[(usize, &str)]) {
+        if block.is_empty() {
+            return;
+        }
         let mut ok = true;
+        let mut block = block.iter();
         let (start_line, name) = loop {
             match block.next() {
-                Some((idx, line)) if line.starts_with("test ") => {
+                Some(&(idx, line)) if line.starts_with("test ") => {
                     break (idx, line["test ".len()..].to_string());
                 }
-                Some((idx, line)) if line.starts_with("test_err ") => {
+                Some(&(idx, line)) if line.starts_with("test_err ") => {
                     ok = false;
                     break (idx, line["test_err ".len()..].to_string());
                 }
                 Some(_) => (),
-                None => continue 'outer,
+                None => return,
             }
         };
         let text: String =
-            itertools::join(block.map(|(_, line)| line).chain(::std::iter::once("")), "\n");
+            block.map(|(_, line)| *line).chain(std::iter::once("")).collect::<Vec<_>>().join("\n");
         assert!(!text.trim().is_empty() && text.ends_with('\n'));
-        res.push((start_line, Test { name, text, ok }))
+        acc.push((start_line, Test { name, text, ok }))
     }
-    res
 }
 
 fn tests_from_dir(dir: &Path) -> Result<Tests> {